1. Field of the Invention
The present invention relates to a numerical control method and a numerical control device for a servo system which is preferably applied to short pitch movement such as for example 50 mm or less.
2. Description of the Related Art
As one indicator considering the motion ability of a robot, there may be mentioned the "tact time". It is considered desirable that this time be shortened as much as possible and in addition that it not be accompanied with unnecessary vibration.
Among the techniques for trying to shorten the tact time for long pitch movement, conventionally (1) attempts to optimize the servo parameters, (2) attempts to optimize an acceleration and deceleration curve (hereinafter also referred to as an acceleration and deceleration pattern), and (3) attempts to optimize an acceleration and deceleration time Tp considering the actuator power (time from the acceleration start time t=0 to when the speed .omega. reaches a peak value .omega..sub.r, hereinafter also referred to as a peak time Tp) have been investigated.
For example, as a method of optimization of the acceleration and deceleration curve with respect to the above-described (2), there has been the proposal made in Japanese Patent Application No. 2-283867 (Japanese Unexamined Patent Publication No. 4-157508). As a method of optimization of the acceleration and deceleration time considering the actuator power with respect to the above-described (3), there has been the proposal in U.S. Pat. No. 5,331,542.
To shorten the movement time for short pitch movement of about 50 mm or less, a technique of raising the frequency characteristic of a servo loop, a technique of simply inputting a step signal .DELTA..theta. of an input position, a technique of adopting various cam curves for an instruction input, etc. have been used.
However, to raise the frequency characteristic of the servo loop, it is necessary to increase the speed of the computation time of the CPU and eliminate or moderate the resonance of the mechanical system in the robot, and therefore if suffers from the disadvantages in that the CPU becomes expensive and a long time is consumed for the attempts to eliminate or moderate the resonance of the mechanical system. Also, it suffers from the disadvantage in that the time for reaching the target position of .DELTA..theta. becomes extremely long if merely a step signal .DELTA..theta. of the input position is input to the servo circuit (in principle, an infinite time is required). Further, it suffers from the disadvantage in that, when various cam curves are adopted for the instruction input, a long time is required for the calculation of the related cam curve and the rising time becomes large in comparison with the eigen acceleration and deceleration time Tp in principle.